1. Field of the Invention
The invention in general relates to electronic circuits, and more particularly to a diode mixer with reduced noise and improved dynamic range.
2. Description of Related Art
A mixer is an electronic circuit which converts an input signal from one frequency to another. Basically, this is accomplished by combining the input signal with the signal from a local oscillator in a non-linear device such as a diode quad. As a result of the process, various frequencies are generated, including sum and difference frequencies. The difference frequency may be selected as the intermediate frequency (IF) for further processing.
In various electronic systems, however, such as in communication and radar systems, two signals, which are very close in frequency, may be simultaneously presented to the mixer input. These two signals combine in the mixer to generate unwanted intermodulation products which have the effect of degrading the dynamic range of the mixer.
It is a primary object of the present invention to provide a mixer having improved dynamic range and a high third order intercept point, which is a figure of merit related to mixer performance.
A microwave diode mixer is provided and includes an RF signal input which receives first and second RF signals of closely related frequencies. A local oscillator signal input receives a local oscillator signal, and the two inputs are connected to a diode quad having four arms, each arm including at least one, and preferably three, diodes.
An RF balun device couples the RF signal input to the diode quad and a local oscillator balun device couples the local oscillator signal input to the diode quad.
A resonant circuit arrangement is connected across the diode quad and has a bandwidth to present a substantially open circuit to the second harmonics of both the first and second RF input signals. This reduces or eliminates intermodulation products which may be produced as a result of the mixing process.
Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and specific example, while disclosing the preferred embodiment of the invention, is provided by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art, from the detailed description.